Ruta Kale

My research is aimed at understanding the physical mechanisms behind the generation and evolution of cosmic rays and magnetic fields on scales ranging from cluster cores to the large scale structure.

Cluster mergers and cosmic ray acceleration

Diffuse radio emission termed as radio halos and relics are among the direct probes of the relativistic electrons and magnetic fields in galaxy clusters. Cluster mergers are closely linked to radio halos and relics but the precise conditions in a particular merger that leads to the generation of these sources is not well understood. A non-detection of such sources towards clusters is also useful to understand the physical conditions that can inhibit the formation of such sources. We are carrying out deep targeted observations of known radio halos and relics to understand the physics of particle acceleration in shocks and turbulence. A statistical study of these sources by surveying a large number of clusters across redshifts and masses is also being carried out.

Life cycle of radio galaxies in and around galaxy clusters

The Brightest Cluster Galaxies (BCGs) and their activity in radio bands are known to influence the physical conditions in cluster cores and are themselves also influenced by the dynamical state of the host cluster. The BCGs and other galaxies like head-tail galaxies in clusters are important sources that deposit relativistic particles in the intra-cluster medium. Studies in the last decade have shown that for the mechanisms of turbulent and shock acceleration to work efficiently, a seed relativistic population is required. Radio galaxies and their remnants can be important sources of the seed relativistic electron population. However the spectra of the seed population are not known well and are often assumed to be simple power-laws. In our work we are modeling spectra of radio galaxies and their remnants under different physical conditions and also obtaining precise broadband measurements of the same.

Non-thermal components of the cosmic web

The inter-galactic medium, that pervades the space between galaxies distributed across the cosmic web, is expected to be magnetised. In the process of large scale structure formation, shocks of Mach numbers reaching ~100 can be driven in the IGM and these can accelerate electrons to relativistic speeds. These energetic electrons and the weak magnetic fields will emit radiation by synchrotron mechanism that can be detectable in radio frequency bands. This emission will be a direct tracer of the non-thermal components of the cosmic web. We are surveying potential sites for detecting the cosmic web using a variety of methods.